<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆</title>
</head>
<body>

<input type="text" placeholder="半径" id="a">
<input type="text" placeholder="周长" id="b">
<input type="text" placeholder="面积" id="c">


<script type="text/javascript">
    var p = Math.PI;
    var n = prompt("请填写内容");
    var c = 2*n*p;
    var d = p*n*n;
    document.querySelector("#a").value = n;
    document.querySelector("#b").value = c;
    document.querySelector("#c").value = d;
</script>
</body>
</html>